<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>呼吸灯</title>
    <style>
        div {
            box-sizing: border-box;
        }
        
        .content {
            width: 360px;
            height: 600px;
            background-color: #333;
            margin: 0 auto;
        }
        
        .box {
            height: 360px;
            padding: 30px;
            animation-duration: 5s;
            animation-timing-function: linear;
            animation-iteration-count: infinite;
            animation-name: outer;
        }
        
        .outer {
            height: 100%;
            border: 5px solid #ccc;
            border-radius: 50%;
            padding: 20px;
            animation-name: inner;
            animation-duration: 5s;
            animation-timing-function: linear;
            animation-iteration-count: infinite;
        }
        
        .inner {
            height: 100%;
            border: 10px solid #fff;
            border-radius: 50%;
        }
        
        @keyframes outer {
            25% {
                padding: 20px;
            }
            50% {
                padding: 30px;
            }
        }
        
        @keyframes inner {
            25% {
                padding: 30px;
            }
            50% {
                padding: 20px;
            }
            75% {
                padding: 30px;
            }
            100% {
                padding: 20px;
            }
        }
    </style>
</head>

<body>
    <div class="content">
        <div class="box">
            <div class="outer">
                <div class="inner"></div>
            </div>
        </div>
    </div>
</body>

</html>